The last thorny soil issue I want to cover is phosphorus.  Steve Solomon's worksheets aim for an equal amount of phosphorus and potassium in the soil, while Michael Phillips thinks more phosphorus is better and recommends building orchard soil to have twice as much phosphorus as potassium.  On the other hand, Harvey Ussery explained that excessively high phosphorus levels cause a decline in mycorrhizal fungi, which means that plants actually have a harder time finding enough phosphorus and can experience a deficiency.  In a worst case scenario, extra phosphorus can even wash into streams and cause eutrophication.  Fertilizing with manure (especially chicken manure) boosts phosophorus levels in the soil quickly, so the question is --- should I be concerned about phosphorus excesses?

Using Solomon's recommended phosphorus levels, it's clear that our native soil is low on phosphorus, but that my preferred horse manure fertilizer has increased levels within the vegetable garden beyond the recommended range.  Of course, if I was using Phillips' goal instead of Solomon's, the vegetable garden would actually be considered deficient in phosphorus like the rest of our homestead.

Solomon backs up Phillips by writing that excess phosphorus is seldom a problem since it will actually increase the nutrient density of your produce.  In fact, in a perfect world, Solomon believes our soil would have 2,000 to 5,000 pounds of phosphorus per acre, at which level enough of the mineral would naturally be released each year to feed our crops with no additional applications of fertilizer.  Based on these figures, I suspect we can carry on with my heavy manuring for another five or so years before phosphorus levels in our vegetable garden exceed biologically healthy amounts.

On the other hand, my readings suggest that excess phosphorus can be an issue in the blueberry patch, where the extra phosphorus can cause some of the same deficiency symptoms you'll notice from high pH or high calcium levels.  I doubt that we're anywhere near that level yet, but it might be worth focusing on building acidic, low phosphorus, low calcium compost for that patch for the future.  And, one of these days, I'll probably have to escape my reliance on off-farm manure and bring our homestead into more of a closed loop.  Stay tuned for a lunchtime series based on How to Grow More Vegetables on that very topic soon.